The objective of the proposed research is to develop conditions for in vitro culture of human mammary cells that would facilitate the use of this human cell system in investigations concerning differentiation and carcinogenesis. We have already etablished conditions that permit short-term growth of human mammary epithelial and myoepithelial cell cultures from many different types of tissues (reduction mammoplasties, benign tumors, mastectomies). We now propose to examine these cells for (1) growth response to different hormones, hopefully to determine optimal concentrations of required nutrient factors and thus promote increased cell growth in vitro; (2) expression of mammary specific properties, such as lactalbumin, casein, and lactose synthesis, in response to different hormonal environments and different culture support systems; (3) properties which may be associated with carcinogenic transformation. These studies may allow us to provide well-characterized cell populations for numerous areas of research.